1. Field of the Invention
This invention relates to an ion-implantation method which is used in the manufacturing process for semiconductor devices such as integrated circuits, and more particularly, to an ion-implantation method for wiring electrodes of a semiconductor device to prevent occurrence of hillocks on the surface of the wiring electrode.
2. Description of the Prior Art
The wiring electrodes disposed in semiconductor devices such as integrated circuits are usually made of aluminum or an aluminum alloy containing a trace amount of an element such as Si, Cu, and Ti. After the wiring electrodes are formed in a given pattern, constituent atoms of the wiring electrodes are moved in such a direction as to reduce internal stresses during heat treatment, which gives rise to convex portions (hereinafter referred to as "hillocks") and concave portions (hereinafter referred to as "voids") in the surface of the wiring electrodes. Of the two occurrences, the hillocks cause insulation failure and electrical shorts between the neighboring wiring electrodes. They will also be responsible for insulation failure and electrical shorts between the above-mentioned wiring electrodes and the wiring electrodes to be formed later in the upper layer over an insulating film.
For example, as shown in FIG. 2, when a wiring electrode 13 is formed in a given pattern on top of an insulating film 12 which covers the semiconductor substrate 11, there occur hillocks 14a and 14b on the surface of the wiring electrode 13 after heat treatment. Particularly, the hillock projecting from the top surface of the wiring electrode 13 is referred to as the vertical hillock 14a. The hillock projecting from the side surface of the wiring electrode 13 is referred to as the lateral hillock 14b. If vertical hillocks 14a occur in a multi-layered wiring structure, when additional wiring electrodes are formed in the upper layer over another insulating film, the insulating film becomes thin in the area where the vertical hillocks 14a project upward. Thus, there is the danger of insulation failure between the lower and the upper wiring electrodes. Also, if lateral hillocks 14b occur, the space between the neighboring wiring electrodes in the same layer becomes narrow in the area where the lateral hillocks 14b project sideward. Thus, there is the danger of electrical shorts between the neighboring wiring electrode in the same layer. As a pattern of wiring electrodes becomes minute due to high density of integrated circuits, the danger of insulation failure and electrical shorts caused by vertical and lateral hillocks becomes marked, which causes a decrease in the reliability of the final product. For this reason, it has become of particular interest in recent years to provide an ion-implantation method used in the manufacturing process of semiconductor devices, which can prevent occurrence of hillocks on the surface of the wiring electrodes.
Usually, in the manufacturing process for semiconductor devices, after the formation of the wiring electrodes 13 in a given pattern, ion implantation is conducted in the direction normal to the top surface of the wiring electrodes 13 as shown in FIG. 3. By the ion implantation of argon, arsenic, or the like in the upper regions 13a near the top surface of the wiring electrodes 13 which are made of aluminum or an aluminum alloy, it is possible to improve the quality of the upper regions 13a. After the quality of the upper regions 13a of the wiring electrodes 13 is improved in this way, there is no occurrence of vertical hillocks 14a on the top surface thereof.
However, even when such a method is used, because ion implantation is conducted in one direction, from above only, the quality of the side regions 13b near the side surfaces of the wiring electrodes 13 cannot be improved. Hence, as shown in FIG. 4, there is occurrence of lateral hillocks 14b from the side surfaces of the wiring electrodes 13. Thus, there remains as yet the danger of electrical shorts between the neighboring wiring electrodes 13, which introduces a problem that it is not possible to ensure sufficient reliability of final products.